1. Field of the Invention
The present invention relates to a design method for a phase shifter, especially to a 90-degree phase shifter used by a quadrature modulator integrated circuit. The present invention implements a design method for a 90-degree phase shifter required by a quadrature modulator integrated circuit by using a RL-RC type microwave network formed by the intrinsic resistors of the transistors of differential amplifiers combined with emitter (source)-degenerative inductor and capacitor.
2. Description of the Related Art
The performance of a quadrature modulator is relative to the precision of the 90-degree phase shift as well as the low amplitude disharmony of the signal from the local oscillator. Many methods for implementing 90-degree phase shift have been suggested now, such as frequency doubling (for example, see H. M. Rein, R. Reimann, and L. Schmidt, “A 3 Gb/s bipolar phase shifter and AGC amplifier,” in IEEE Int. Solid-State Circuits Conf. Tech. Dig., 1989, pp. 144-145.; K. Maemura, Y. Kohno, H. Nakano, T. Shimura, K. Oki, H. Ishida, and O. Ishihara, “The 200 MHz- and 1.5 GHz-band GaAs monolithic quadrature modulator ICs,” in Gallium Arsenide Integrated Circuit Symp. Dig., 1990, pp. 283-286.; J. Itoh, T. Nakatsuka, K. Sato, Y. Imagawa, T. Uda, T. Yokoyama, M. Maeda, and O. Ishikawa, “A low distortion GaAs quadrature modulator IC,” in IEEE Radio-Frequency Integrated Circuit Symp. Dig., 1998, pp. 55-58). The use of frequency doubling is advantageous to the precise control of the phase shift, however the current consumption is higher. Another method is the use of RC integrator/CR differentiator (for example, see M. Steyaert, and R. Roovers, “A 1-GHz single-chip quadrature modulator,” IEEE J. Solid-State Circuits, vol. 27, pp. 1194-1197, August 1992.; K. Yamamoto, K. Maemura, N. Andoh, and Y. Mitsui, “A 1.9-GHz-band GaAs direct-quadrature modulator IC with a phase shifter,” IEEE J. Solid-State Circuits, vol. 28, pp. 994-1000, October 1993.; U.S. Pat. No. 5,694,093 entitled “Wideband IQ modulator with RC/CR automatic quadrature network”). The use of RC integrator/CR differentiator is advantageous to the simple design as well as small current consumption, however the implementation loss is higher.
In addition to the above two methods, LC high pass/low pass filter method, RC full pass filter method, ring oscillator method, multi-phase filter method, etc. can also be used, however they still have the disadvantages of high implementation loss, difficult to be integrated in an integrated circuit, complex design, the difficulty of precise control of the phase shift, high current consumption, etc.
In summary, the common disadvantage for the above design methods is high implementation loss, it is because resistors used by existing 90-degree phase shifters are real resistors.